The 1912 Le Chemineau derailleur was developed by Joanny Panel, based on a prototype built by Paul de Vivie. In many ways it defined many of the attributes of a modern derailleur. It has a guide pulley that moves in and out, moving the chain across a sprocket cluster, it has a sprung arm that provides chain tension with a tension pulley on it, and it was controlled by a single cable, working in opposition to a spring.

Eerily the centre to centre distance on the pulley arm is 75mm - a measurement commonly found today. The tension pulley has 10 teeth - another recurring theme.

Unfamiliar to us today are the ideas of mounting the derailleur on the underside of the chainstay, and of using a toggle chain to pull the derailleur along a rod - but both these ideas would have been totally mainstream as late as 1960.

This, rather beautifully preserved, example is one of three in this collection. I think that this example is a later version than the other two - possibly from the late 1920s. Its pulley arm is round in cross section and has a 'D' shaped loop at the top to take the spring. It also has fantastic plating and its other parts are slightly different from my two other examples.

My guess is that the tension pulley is not original - but I am not sure about this. It looks like a Cyclo part - but unlike most after-market Cyclo parts, it does not have any Cyclo branding on it. During the 1930s Chemineau did use increasingly fancy flanged tension pulleys - and both Le Chemineau and Cyclo were based in St-Étienne - so it is not impossible that Chemineau fitted Cyclo pulleys at some point. However Joanny Panel was also known to have a long running, and highly personal feud, with Albert Raimond of Cyclo.

• Derailleur brands: Chemineau
• Themes: Who invented the derailleur?
• Country: France
• Date of introduction: 1912
• Date of this example: unknown
• Model no.: unknown
• Weight: 314g including toggle chain but excluding mounting plate and spring
• Maximum cog: 28 teeth?
• Total capacity: 28 teeth?
• Pulley centre to centre: 75mm
• Index compatibility: friction
• Chain width: 1/8”
• Logic: low normal
• B pivot: none
• P pivot: sprung
• Materials: steel